Polystyrene is a plastic used in many applications. The plastic can be extruded, injection molded, or blow molded to make objects like plastic cups and utensils, and casings for CDs. Polystyrene can also be formed with a rubber such as polybutadiene to make high impact polystyrene, or HIPS, which is more resistant to impact than normal polystyrene. HIPS can be used in toys, casings for appliances, and containers for food and medical supplies. One of the most recognizable forms of polystyrene is its foamed form, which can be used in packing materials and can be molded into containers, plates, cups and other shapes.
The monomer styrene is commonly produced via the dehydrogenation of ethylbenzene. This reaction can have several drawbacks, one being the formation of side products, such as benzene, toluene, and unreacted ethylbenzene. Another drawback is that ethylbenzene and styrene have similar boiling points, which can make their separation difficult.
Ethylbenzene, in turn, is generally produced via the alkylation of benzene with ethylene. The reaction can create several side products, such as polyalkylated benzene. One significant drawback to this reaction is the relatively expensive reactants that are required. Both ethylene and benzene can be obtained from refined petroleum. Ethylene is obtained predominantly from the thermal cracking of hydrocarbons, such as ethane, propane, butane, or naphtha, and generally goes through several cycles of distillation to obtain a certain purity level. Ethylene from these sources can include a variety of undesired products, including diolefins and acetylene, which can be costly to separate from the ethylene. Thermal cracking and separation technologies for the production of relatively pure ethylene can result in significant production costs.
Other methods for producing styrene include the oxidative coupling of hydrocarbons. This oxidative coupling reaction takes place in the presence of oxygen at elevated temperatures. Using an oxidative coupling reaction, styrene can be produced from toluene and methane. Historically, however, this process has suffered from low selectivity. Such low selectivity can lead to increased costs in order to achieve the desired product amount.
The costs associated with the production of polystyrene can be considered significant. Production relying on the alkylation of benzene with ethylene and the dehydrogenation of ethylbenzene for obtaining the monomer styrene can be cost intensive. Other methods, such as oxidative reactions, may use less expensive starting materials, however, these methods can suffer from low product selectivity. It would be desirable to have alternate methods for the production of ethylbenzene and styrene that increase product selectivity and that are consequently more economical.